Optical space switch device

ABSTRACT

The invention provides an optical space switch device which provides variable interconnection of one- or two-dimensionally spatially multiplexed optical signals. The optical space switch device comprises a plurality of optical space switch stages stacked to form a multi-input multi-output optical space switch. Each of the optical space switch stages comprises a plurality of 2-input 2-output optical switches, each of which comprises a polarization control layer and an optical path shifting layer. The optical path shifting layer has a bypass mode in which it outputs beams of light along optical axes and an exchange mode in which it shifts beams of light by diffraction.

This application is a division of application Ser. No. 07/910,779, filedJul. 08, 1992, now U.S. Pat. No. 5,430,561.

BACKGROUND OF THE INVENTION

This invention relates to an optical space switch device which providesvariable interconnection of one- or two-dimensionally spatiallymultiplexed optical signals.

In recent years, the requirement has been and is increasing for transferof image data of a large capacity of 4 kilobytes to 6 megabytes or so byway of a very high speed transmission line of 10 gigabits/second or so.It has been proposed to employ an optical space switch device as avariably interconnectable cross connecting device to achieve suchtransfer.

Meanwhile, attention has been and is paid to an optical space switchdevice as it can be utilized also for other applications wherein asubsystem such as a coupling network between processors and/or memoriesof a parallel processing computer or a multistage switch for an ATMexchange is realized with optical channels.

As an optical space switch device of the type mentioned, an opticalswitch has conventionally been proposed and is disclosed, for example,in APPLIED OPTITCS, Vol. 29, No. 26, pp. 3848-3854, Sep. 10, 1990, whichincludes a combination of a polarization controlling element formed froma liquid crystal material and a device providing a polarized lightseparating function and employing a hologram.

Another optical switch has been proposed and is disclosed in PhotonicSwitching II, Proceedings of the International Topical Meeting, Kobe,Japan, Apr. 12-14, 1990, which includes a combination of a polarizationcontrolling planar element such as a liquid crystal panel for receivinga planar input and a routing element employing a birefringent crystal.

Also an optical space switch has been proposed and is disclosed inPhotonic Switching, Vol. 8, Proceedings of the International TopicalMeeting, Salt Lake City, Utah, Mar. 6-8, 1991, which includes a firstreflecting block including a combination of a polarized light separator,a polarization controller, a quarter-wave (λ/4) plate and an opticalpath modifying element, and a second reflecting block including aquarter-wave plate and a reflecting mirror.

Also an optical crossbar switch device has been proposed wherein opticalcrossbar switches are disposed in a matrix on a waveguide formed on adielectric (LiNbO₃) substrate.

However, such conventional optical space switch devices as describedabove are disadvantageous in that they are complicated in structure andexpensive and require, because a polishing step is necessary, a greatnumber of working steps.

Further, while the conventional optical space switch device of the typewhich includes a first reflecting block including a polarized lightseparator, a polarization controller, a quarter-wave plate and anoptical path modifying element and a second reflecting block including aquarter-wave plate and a reflecting mirror employs a prism array as theoptical path modifying element, when it is designed so as to receivemultichannel beams as an input thereto, the prism array has acorrespondingly great size, and besides there is the possibility thatthe insertion loss and the crosstalk may be increased by an increase ofthe number of optical paths and an increase of the difference amonglengths of the optical paths by beam routes. It is furtherdisadvantageous in that it can assume only 2-input 2-outputconfiguration.

Also there is a disadvantage that it is impossible to handle atwo-dimensional signal (planar input).

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an optical spaceswitch device which can assume a multi-input multi-output configurationreadily and the insertion error and the crosstalk are minimized.

It is another object of the present invention to provide an opticalspace switch device wherein components are made as common as possible sothat the number of different kinds of parts in production is reduced.

It is a further object of the present invention to provide an opticalspace switch device wherein the distance between channels is minimized.

It is a still further object of the present invention to provide anoptical space switch device wherein positioning for production orassembly is facilitated.

It is a yet further object of the present invention to provide anoptical space switch device which can implement, using a 2-input2-output optical switch having polarization controlling means andoptical path shifting means as a basic switch, a polarizationcontrolling algorithm which affords non-blocking cross connect routing.

In order to attain the objects, according to one aspect of the presentinvention, there is provided an optical space switch device, comprisinga plurality of optical space switch stages stacked to form a multi-inputmulti-output optical space switch, including a plurality of 2-input2-output optical switches, each of the 2-input 2-output optical switchesincluding polarization controlling means, disposed on two paralleloptical axes, for switching a polarization plane between two orthogonalpolarization directions, and optical path shifting means for outputtingtwo beams of light along the corresponding optical axes when thepolarization plane is controlled to be in one of the orthogonalpolarization by the polarization controlling means and for outputtingtwo beams of light along the other optical axes when the polarizationplane is controlled to be in the other of the orthogonal polarization bythe polarization controlling means, the 2-input 2-output opticalswitches of the optical space switch stages are disposed so as to extendplanes of the parallel optical axes in parallel to each other.

The polarization controlling means comprises a pair of transparentelectrodes and a liquid crystal held between the transparent electrodessuch that a voltage may be applied across the liquid crystal element bythe transparent electrodes to control a polarizing condition of lightpassing through the liquid crystal element, and the polarizationcontrolling means is segmented in accordance with an arrangement ofchannels such that the segments are controlled independently of eachother.

Preferably, the optical path shifting means comprises first and seconddiffraction grating layers disposed in a parallel and spacedrelationship from each other, each of the diffraction gratings of thefirst and second diffraction grating layers being constituted from apair of planar diffraction gratings having different grating vectors,the optical path shifting means being operable to shift a beam ofS-polarized light by diffraction by the first and second diffractiongrating layers but transmit a beam of P-polarized light through thefirst and second diffraction grating layers, each of the first andsecond diffraction grating layers being constructed such that aplurality of pairs of planar diffraction grating segments havingdifferent grating vectors in each pair are arranged two-dimensionallysuch that a beam of light may be shifted between adjacent channels inaccordance with a polarization condition thereof.

Prefrably, the optical path shifting means comprises first and seconddiffraction grating layers disposed in a parallel and spacedrelationship from each other, each of the diffraction gratings of thefirst and second diffraction grating layers being constituted from apair of planar diffraction gratings having different grating vectors,the optical path shifting means being operable to shift a beam ofS-polarized light by diffraction by the first and second diffractiongrating layers but transmit a beam of P-polarized light through thefirst and second diffraction grating layers, each of the optical spaceswitch stages being constituted from the polarizing controlling meansand first and second diffraction grating layers stacked integrallywithout having an air layer therein, the optical space switch stagesbeing stacked integrally without having an air layer therein to form themulti-input multi-output optical space switch.

The optical space switch device may further comprise collimate meansprovided on the light input side of the optical space switch stages forconverting incident light to the optical space switch stages intoparallel light, and light converging means provided on the light outputside of the optical space switch stages for converging emergent lightfrom the optical space switch stages.

According to another aspect of the present invention, there is providedan optical space switch device, comprising first and second opticalspace switch stages stacked in a condition rotated by 90 degrees fromeach other to form a 4-input 4-output optical space switch, including apair of 2-input 2-output optical switches, each of the 2-input 2-outputoptical switches including polarization controlling means, disposed ontwo parallel optical axes, for switching a polarization plane betweentwo orthogonal polarization directions, and optical path shifting meansfor outputting two beams of light along the corresponding optical axeswhen the polarization plane is controlled to be in one of the orthogonalpolarization by the polarization controlling means and for outputtingtwo beams of light along the other optical axes when the polarizationplane is controlled to be in the other of the orthogonal polarization bythe polarization controlling means, the 2-input 2-output opticalswitches of the first and second optical space switch stages aredisposed so as to extend incident faces in parallel to each other.

According to a further aspect of the present invention, there isprovided an optical space switch device, comprising four optical spaceswitch stages stacked to form an 8-input 8-output Banyan network typeoptical space switch and each including four 2-input 2-output opticalswitches, each of the 2-input 2-output optical switches includingpolarization controlling means, disposed on two parallel optical axes,for switching a polarization plane between two orthogonal polarizationdirections, and optical path shifting means for outputting two beams oflight along the corresponding optical axes when the polarization planeis controlled to be in one of the orthogonal polarization by thepolarization controlling means and for outputting two beams of lightalong the other optical axes when the polarization plane is controlledto be in the other of the orthogonal polarization by the polarizationcontrolling means, the 2-input 2-output optical switches of the opticalspace switch stages are disposed in parallel so as to extend incidentfaces in parallel to each other, and wherein, where the distance betweenmost adjacent channels in a light inputting plane is represented by dand the coordinates of the origin 0 are represented by (0, 0), thechannel 0 is disposed at (0, d); the channel 1 at (d, d); the channel 2at (d, 2d); the channel 3 at (2d, 2d); the channel 4 at (d, 0); thechannel 5 at (2d, 0); the channel 6 at (2d, d); and the channel 7 at(3d, d), and beam shifting structures between the channel 0--channel 4,the channel 1--channel 5, the channel 2--channel 6 and the channel3--channel 7 are provided at the first optical space switch stage; beamshifting structures between the channel 0--channel 2, the channel1--channel 3, the channel 4--channel 6 and the channel 5--channel 7 areprovided at both of the second and third optical space switch stage; andbeam shifting structures between the channel 0--channel 1, the channel2--channel 3, the channel 4--channel 5 and the channel 6--channel 7 areprovided at the fourth optical space switch stage.

The optical space switch device may further comprise means interposedbetween the third and fourth optical space switch stages for rotating apolarization plane of polarized light by 45 degrees.

According to a still furher aspect of the present invention, there isprovided an optical space switch device, comprising eleven optical spaceswitch stages stacked to provide an equivalent circuit structure of an11 stage cross Banyan network, including a plurality of 2-input 2-outputoptical switches, each of the 2-input 2-output optical switchesincluding polarization controlling means, disposed on two paralleloptical axes, for switching a polarization plane between two orthogonalpolarization directions, and optical path shifting means for outputtingtwo beams of light along the corresponding optical axes when thepolarization plane is controlled to be in one of the orthogonalpolarization by the polarization controlling means and for outputtingtwo beams of light along the other optical axes when the polarizationplane is controlled to be in the other of the orthogonal polarization bythe polarization controlling means, the 2-input 2-output opticalswitches of the optical space switch stages are disposed so as to extendplanes provided by the parallel optical axes in parallel to each other,and wherein, where the distance between most adjacent channels in alight inputting plane is represented by d and the coordinates of theorigin 0 are represented by (0, 0), the channel 0 is disposed at (0, 0);the channel 1 at (0, -2d); the channel 2 at (2d, 0); the channel 3 at(2d, -2d); the channel 4 at (d, -d); the channel 5 at (d, -3d); thechannel 6 at (3d, -d); the channel 7 at (3d, -3d); the channel 8 at (d,0); the channel 9 at (d, -2d); the channel 10 at (3d, 0); the channel 11at (3d, -2d); the channel 12 at (0, -d); the channel 13 at (0, -3d); thechannel 14 at (2d, -d); and the channel 15 at (2d, -3d), and a beam canbe shifted between the channels 0--2, 4--6, 1--3, 5--7, 8--10, 12--14,9--11 and 13--15 at the first, fourth, seventh and tenth optical spaceswitch stages; a beam can be shifted between the channels 0--1, 4--5,2--3, 6--7, 12--13, 8--9, 14--15 and 10--11 at the second, fifth, eighthand eleventh optical space switch stages; a beam can be shifted betweenthe channels 0--4, 1--5, 2--6, 3--7, 8--12, 9--13, 10--14 and 11--15 atthe third and ninth optical space switch stages; and a beam can beshifted between the channels 0--8, 12--4, 1--9, 13--5, 2--10, 14--6,3--11 and 15--7 at the sixth optical space switch stage; and where NB(I)is the Ith bit of the binary represented address of each node at eachstage, FB(J) is the Jth bit of the binary represented address of adestination node, PS is the polarization of the input beam at each nodehaving the value "0" when the polarization of the input beam to the nodeis P-polarization but having the value "1" when such polarization isS-polarization, and SC is the state of the polarization controllingswitch, polarization switch setting is provided such that, for thefirst, fourth, seventh and tenth stages,

    SC=PS XOR (NB(3) XOR FB(3))

for the second, fifth, eighth and eleventh stages.

    SC=PS XOR (NB(4) XOR FB(4))

for the third and ninth stages,

    SC=PS XOR (NB(2) XOR FB(2)), and

for the sixth stage,

    SC=PS XOR (NB(1) XOR FB(1))

where X XOR Y signifies exclusive OR of X and Y.

According to a yet further aspect of the present invention, there isprovided an optical space switch device, comprising nine optical spaceswitch stages stacked to provide an equivalent circuit structure of a 9stage expanded modified Banyan network, including a plurality of 2-input2-output optical switches, each of the 2-input 2-output optical switchesincluding polarization controlling means, disposed on two paralleloptical axes, for switching a polarization plane between two orthogonalpolarization directions, and optical path shifting means for outputtingtwo beams of light along the corresponding optical axes when thepolarization plane is controlled to be in one of the orthogonalpolarization by the polarization controlling means and for outputtingtwo beams of light along the other optical axes when the polarizationplane is controlled to be in the other of the orthogonal polarization bythe polarization controlling means, the 2-input 2-output opticalswitches of the optical space switch stages are disposed so as to extendplanes provided by the parallel optical axes in parallel to each other;and wherein, where the distance between most adjacent channels in alight inputting plane is represented by d and the coordinates of theorigin 0 are represented by (0, 0), the channel 0 is disposed at (0, 0);the channel 1 at (d, -d); the channel 2 at (0, -2d); the channel 3 at(d, -3d); the channel 4 at (2d, 0); the channel 5 at (3d, -d); thechannel 6 at (2d, -2d); the channel 7 at (3d, -3d); the channel 8 at (d,0); the channel 9 at (0, -d); the channel 10 at (d, -2d); the channel 11at (0, -3d); the channel 12 at (3d, 0); the channel 13 at (2d, -d); thechannel 14 at (3d, -2d); and the channel 15 at (2d, -3d), and a beam canbe shifted between the channels 0--4, 1--5, 2--6, 3--7, 8--12, 9--13,10--14 and 11--15 at the first and sixth optical space switch stages; abeam can be shifted between the channels 0--2, 1--3, 4--6, 5--7, 9--11,8--10, 13--15 and 12--14 at the second, third, seventh and eighthoptical space switch stages; a beam can be shifted between the channels0--1, 2--3, 4--5, 6--7, 8--9, 10--11, 12--13 and 14--15 at the fourthand ninth optical space switch stages; and a beam can be shifted betweenthe channels 0--8, 1--9, 2--10, 3--11, 4--12, 5--13, 6--14 and 7--15 atthe fifth optical space switch stage; and where NB(I) is the Ith bit ofthe binary represented address of each node at each stage, FB(J) is theJth bit of the binary represented address of a destination node, PS isthe polarization of the input beam at each node having the value "0"when the polarization of the input beam to the node is P-polarizationbut having the value "1" when such polarization is S-polarization, andSC is the state of the polarization controlling switch, polarizationswitch setting is provided such that, for the first, third, fourth,sixth, eighth and ninth stages,

    SC=PS XOR (NB(M) XOR FB(M))

where M=2, 3, 4, 2, 3, 4 in this order for the stages,

for the second and seventh stages,

    SC=PS XOR (NB(3) XOR FB(3)), and

for the fifth stage,

    SC=PS XOR (NB(1) XOR FB(1))

where X XOR Y signifies exclusive OR of X and Y.

According to a yet further aspect of the present invention, there isprovided an optical space switch device, comprising a plurality ofoptical space switch stages stacked to provide an equivalent circuitstructure of an 8-input modified Banyan network wherein four suchoptical space switch stages are stacked, the optical space switch devicehaving an equivalent circuit structure of a 2^(n) -input expandedmodified Banyan network formed by expanding the 8-input modified Banyannetwork by combination of a plurality of such 8-input modified Banyannetworks, each of the optical space switch stages including a pluralityof 2-input 2-output optical switches, each of the 2-input 2-outputoptical switches including polarization controlling means, disposed ontwo parallel optical axes, for switching a polarization plane betweentwo orthogonal polarization directions, and optical path shifting meansfor outputting two beams of light along the corresponding optical axeswhen the polarization plane is controlled to be in one of the orthogonalpolarization by the polarization controlling means and for outputtingtwo beams of light along the other optical axes when the polarizationplane is controlled to be in the other of the orthogonal polarization bythe polarization controlling means, the 2-input 2-output opticalswitches of the optical space switch stages are disposed so as to extendplanes provided by the parallel optical axes in parallel to each other;and wherein, in each of the 8-input modified Banyan networks, whereNB(I) is the Ith bit of the binary represented address of each node ateach stage. FB(J) is the Jth bit of the binary represented address of adestination node, PS is the polarization of the input beam at each nodehaving the value "0" when the polarization of the input beam to the nodeis P-polarization but having the value "1" when such polarization isS-polarization, and SC is the state of the polarization controllingswitch, polarization switch setting is provided such that, for thefirst, third and fourth stages,

    SC=PS XOR (NB(M) XOR FB(M))

where M=1, 2, 3 in this order for the stages, and for the second stage,

    SC=PS XOR FB(2)

where X XOR Y signifies exclusive OR of X and Y.

Preferably, the number of inputs is given by 2^(N+2), N being a positiveintegral number, and, when N is an odd number, a second arrangementwhich is horizontally symmetrical with an original arrangement of2^(N+2) channels is first made separately, and then channel numbersequal to or greater than 2^(N+2) are applied to the second channelarrangement while maintaining the order of rows and the order of columnsin each row of the original channel arrangement, whereafter the twochannel arrangements are overlaid to make a further arrangement of2^(N+3) channels, thereby expanding the 8-input modified Banyan networkby combination of a plurality Of such 8-input modified Banyan networks.

Preferably, the number of inputs is given by 2^(N+2), N being a positiveintegral number, and, when N is an even number, a second arrangementwhich is the same as an original arrangement of 2^(N+2) channels is madeseparately, and then channel numbers equal to or greater than 2^(N+2)are applied to the second channel arrangement while maintaining theorder of rows and the order of columns in each row of the originalchannel arrangement, whereafter the two channel arrangements areoverlaid in a displaced condition by one half the minimum channeldistance d in two orthogonal directions to make a further arrangement of2^(N+3) channels, thereby expanding the 8-input modified Banyan networkby combination of a plurality of such 8-input modified Banyan networks.

According to a yet further aspect of the present invention, there isprovided an optical space switch device, comprising a 2-input 2-outputoptical switch including polarization controlling means, disposed on twoparallel optical axes, for switching a polarization plane between twoorthogonal polarization directions, and optical path shifting means foroutputting two beams of light along the corresponding optical axes whenthe polarization plane is controlled to be in one of the orthogonalpolarization by the polarization controlling means and for outputtingtwo beams of light along the other optical axes when the polarizationplane is controlled to be in the other of the orthogonal polarization bythe polarization controlling means.

Preferably, the optical path shifting means comprises first and seconddiffraction grating layers disposed in a parallel and spacedrelationship from each other, each of the diffraction gratings of thefirst and second diffraction grating layers being constituted from apair of planar diffraction gratings having different grating vectors,the optical path shifting means being operable to shift a beam ofS-polarized light by diffraction by the first and second diffractiongrating layers but transmit a beam of P-polarized light through thefirst and second diffraction grating layers.

The diffraction grating of each of the diffraction grating layers hasgrating stripes inclined in a thicknesswise direction so that a flux oflight incident perpendicularly thereto may be deflected by a requiredangle by Bragg diffraction.

Preferably, the diffraction grating of each of the diffraction gratinglayers has an asymmetrical cross section so that a flux of lightincident perpendicularly thereto may be deflected by a required angle byBragg diffraction. The angle at which the diffraction grating of each ofthe diffraction grating layers deflects a flux of light incidentperpendicularly thereto by Bragg may be set to 48.2 degrees. Preferably,the diffraction grating of each of the diffraction grating layers isconstructed such that the diffraction factor modulation Δn, wavelength λand thickness D thereof may satisfy the equation

    Δn·D·cos48.2°=π·λ.

Preferably, a holographic diffraction grating is employed for thediffraction grating layers.

The polarization controlling means may comprise a pair of transparentelectrodes and a liquid crystal held between the transparent electrodessuch that a voltage may be applied across the liquid crystal element bythe transparent electrodes to control a polarizing condition of theliquid crystal element, and the diffraction grating layers are formedintegrally on a substrate on which the transparent electrodes are formedwith the liquid crystal element held therebetween.

Preferably, each of the first and second diffraction grating layers isconstructed such that adjacent regions of the diffraction grating havingan equal spatial frequency and having grating vectors of a samedirection are joined together to eliminate a boundary therebetween.

Preferably, each of the first and second diffraction grating layers isconstructed such that all channels are surrounded by a boundary having apredetermined width in which no diffraction grating is formed.

Preferably, the first diffraction grating layer is formed integrally ona face of a transparent flat plate, and the second diffraction gratinglayer is formed integrally on the other face of the transparent flatplate.

With the optical space switch devices, since it comprises a plurality ofoptical space switch stages stacked to construct a multi-inputmulti-output optical space switch and each comprising a plurality of2-input 2-output optical switches having a bypass mode and an exchangemode and disposed such that planes of respective two parallel opticalaxes thereof may extend in parallel to each other and particularly theoptical path modifying portion of each optical space switch can beformed in a stacked structure of a polarization controlling element anddiffraction gratings, it is simple in construction and can beconstructed suitably for two-dimensionally arranged channels.

Further, while each of the diffraction grating layers constituting theoptical space switch stages has a plurality of segments, most of themare common although they are different in direction or front-backorientation, and advantageously the number of different types of partsis not so much as the number of diffraction grating layers involved.

Further, since modification of optical paths at each stage takes placebetween adjacent channels, the lengths of the optical paths requiredtherefor are minimized and it is possible to reduce the distance betweenchannels.

Further, where the diffracting grating layers are provided integrally onthe opposite faces of the transparent flat plate, positioning of theoptical switch can be performed readily upon production or assembly.

Besides, a small size multi-input multi-output optical space switchdevice of the thin layer stacked structure can be constructed readily bycombination of a polarization controlling element and hologramdiffraction elements thereby to optically realize non-blocking crossconnect routing of a non-Banyan network (including an expanded modifiedBanyan network) which is reduced in insertion loss and crosstalk.

Further objects, features and advantages of the present invention willbecome apparent from the following detailed description when read inconjunction with the accompanying drawings in which like parts orelements are denoted by like reference characters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a schematic view showing construction of a 2-input 2-outputoptical switch device according to a first preferred embodiment of thepresent invention;

FIG. 1(b) is a diagrammatic view illustrating a manner of representingan abbreviation mark of the 2-input 2-output optical switch device ofFIG. 1(a);

FIG. 2 is a schematic view showing construction of a modification to the2-input 2-output optical switch device of FIG. 1(a);

FIG. 3 is a diagram showing an efficiency characteristic of aholographic diffraction grating;

FIG. 4 is a schematic sectional view of a holographic diffractiongrating;

FIG. 5 is a diagrammatic view illustrating a shift of a beam caused by avariation of the wavelength;

FIG. 6 is a diagrammatic view illustrating wiring between channels of a4-input 4-output optical space switch device as a second preferredembodiment of the present invention;

FIGS. 7(a) and 7(b) are diagrammatic views illustrating wiring schemesat different stages of the 4-input 4-output optical space switch deviceof FIG. 6;

FIGS. 8(a) to 8(f) are schematic illustrations showing components at thedifferent stages of the 4-input 4-output optical space switch device ofFIG. 6;

FIG. 9 is a schematic view showing a stacking structure of the 4-input4-output optical space switch device of FIG. 6;

FIG. 10 is a diagrammatic view illustrating wiring between channels ofan 8-input 8-output optical space switch device as a third preferredembodiment of the present invention;

FIGS. 11(a) to 11(d) are diagrammatic views illustrating wiring schemesat different stages of the 8-input 8-output optical space switch deviceof FIG. 10;

FIGS. 12(a) to 12(i) are schematic illustrations showing componentelements at the different stages of the 8-input 8-output optical spaceswitch device of FIG. 10;

FIG. 13 is a schematic view showing a stacking structure of the 8-input8-output optical space switch device of FIG. 10;

FIG. 14 is a schematic illustrating showing another holographicdiffraction grating layer;

FIG. 15 is an equivalent circuit diagram of an 11 stage cross Banyannetwork according to a fourth preferred embodiment of the presentinvention;

FIG. 16 is a diagrammatic representation illustrating a two-dimensionalarrangement of input beams to the 11 stage 16×16 cross connect switch ofthe fourth preferred embodiment;

FIG. 17 is a diagrammatic view illustrating parallel channel arrays atdifferent stages constituting the 11 stage 16×16 cross connect switch;

FIG. 18 is an equivalent circuit diagram of a 9 stage expanded modifiedBanyan network according to a fifth preferred embodiment of the presentinvention;

FIG. 19 is a diagrammatic representation illustrating a two-dimensionalarrangement of input beams to the 9 stage 16×16 cross connect switch ofthe fifth preferred embodiment of the present invention;

FIG. 20 is a diagrammatic view illustrating parallel channel arrays atdifferent stages constituting the 9 stage 16×16 cross connect switch;

FIG. 21 is a schematic view showing a three-dimensional structure of the9 stage modified Banyan network of FIG. 18;

FIG. 22 is a schematic view showing an exemplary stacking structure ofthe 9 stage modified Banyan network of FIG. 18;

FIG. 23 is a block diagram showing an exemplary equivalent circuit of a2^(n) stage expanded Banyan network according to a sixth preferredembodiment of the present invention; and

FIG. 24 is a diagrammatic view illustrating a manner of expanding atwo-dimensional arrangement configuration when 2^(N+2) inputs areinvolved in the cross connect switch of the sixth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(a) Description of the First Embodiment

Referring first to FIG. 1(a), there is shown a 2-input 2-output opticalswitch as a unit switch of an optical space switch device of the presentinvention. The 2-input 2-output optical switch shown includespolarization controlling means 10 disposed in two parallel optical axes(one of which will be hereinafter referred to as channel A and the otheras channel B) for switching a linear polarization plane betweenconditions of two orthogonal directions, and optical path shifting means20 also disposed in the two parallel optical axes for shifting opticalpaths by diffraction so that a flux of light propagating along any oneof the optical axes may propagate, after it passes the optical pathshifting means 20, along the other optical axis when the light is in oneof the conditions of the two polarization directions.

Here, though not particularly shown, the polarization controlling means10 is constructed as means wherein liquid crystal is held between a pairof transparent electrodes 10A and 10B such that a voltage may be appliedthereacross from the latter so that it may control a condition of lightto be polarized thereby.

Meanwhile, the optical path shifting means 20 includes a firstdiffraction grating layer 22 and a second diffraction grating layer 23disposed in a parallel and spaced relationship from each other with atransparent flat plate 21, such as a glass plate, interposedtherebetween. The diffraction grating of each of the first and seconddiffraction grating layers 22 and 23 is composed of a pair of planediffraction gratings having different grating vectors. When a beam ofS-polarized light is introduced into the optical path shifting means 20,it is diffracted first by the first diffraction grating layer 22 andthen by the second diffraction grating layer 23 so that it is shiftedfrom the channel A to the channel B or vice versa, but when a beam ofP-polarized light is introduced into the optical path shifting means 20,it passes through both of the first and second diffraction gratinglayers 22 and 23. A diffraction grating layer which employs aholographic diffraction grating is used for each of the diffractiongrating layers 22 and 23.

It is to be noted that, in this instance, the optical path shiftingmeans 20 is constructed such that grating stripes of the diffractiongrating layers 22 and 23 are inclined in a thicknesswise direction sothat the diffraction gratings may deflect a flux of light incidentperpendicularly thereto by a predetermined angle by Bragg diffraction.

However, each of the diffraction grating layers 22 and 23 may otherwisebe constructed such that, as shown in FIG. 2, the cross section of thegrating thereof has an assymmetrical shape such that the diffractiongrating may deflect a flux of light incident perpendicularly thereto bya predetermined angle by Bragg diffraction.

In the modified 2-input 2-output optical switch shown in FIG. 2, thediffraction grating layer 22 is formed integrally on a substrate 11wherein a pair of transparent electrodes are formed on the oppositefaces of a liquid crystal. This facilitates production of the opticalswitch.

Further, the first diffraction grating layer 22 may be providedintegrally on one face of the transparent flat plate 21 while the seconddiffraction grating layer 23 is provided integrally on the opposite faceof the transparent flat plate 21. This facilitates accurate positioningof the optical switch upon assembly.

It is to be noted that, in FIGS. 1(a) and 2, the diffraction gratinglayers 22 and 23 are shown with a greater thickness than an actual onein order to clearly indicate presence of them, but the ratios inthickness among the substrate 11, transparent flat plate 21 anddiffraction grating layers 22 and 23 are not such as seen from FIG. 1(a)or 2.

In this manner, with either of the 2-input 2-output optical switchesshown in FIGS. 1(a) and 2, optical paths can be exchanged between thetwo parallel channels A and B. In particular, when two beams of linearlypolarized light are introduced from the channels A and B into the2-input 2-output optical switch, switching whether the beams advancestraightforwardly without exchanging the optical paths thereof (bypassmode) or advance exchanging the optical paths thereof (exchange mode)can be performed depending upon whether the light has a polarizationplane parallel to the plane of FIG. 1(a) or 2 (P-polarized light) or hasanother polarization plane perpendicular to the plane of FIG. 1(a) of 2(S-polarized light).

Then, in order to positively change the polarization condition from S toP or reversely from P to S, the polarization controlling means 10described above is used, and in order to diffract a beam of light inaccordance with a polarization condition, the first and seconddiffraction grating layers 22 and 23 are used.

Further, optical channels parallel to each other and a constructionwherein planar means are stacked perpendicular to the optical axes makeit possible to achieve, using the stack as a unit, a structure wherein aplurality of such units are arranged two-dimensionally and in parallel.Further, a structure constructed in this manner can be placed one onanother into a plurality of stages in the direction of the optical axes,which is advantageous in constructing a multichannel switch.

It is to be noted that, while a holographic diffraction grating isemployed for the first and second diffraction grating layers 22 and 23as described above, a plane grating composed of parallel stripes is usedas the diffraction grating such that it diffracts light incidentperpendicularly thereto toward the other channel.

In this instance, the stripes in a cross section of the diffractiongrating are inclined as described above in order to achieve efficientBragg diffraction of light. Further, since the diffracted directions oflight are different between the channels A and B, the slantingdirections of the grating stripes are changed symmetrically in the twodifferent regions. In other words, the slating directions aresymmetrical with respect to a boundary plane between the channels.

Further, the holographic diffraction gratings are produced in specialconditions in order that they may act on S-polarized light so that itmay be diffracted but they may not act on P-polarized light so that itmay pass therethrough. The conditions will be hereinafter described.

It is to be noted that, for the convenience of description below, amanner wherein the construction of FIG. 1(a) is viewed in the incomingdirection of light is represented in an abbreviated symbol wherein twodark dots are interconnected by a line as shown in FIG. 1(b). Each darkdot indicates a channel, and a line segment indicates that optical pathscan be exchanged between channels at the opposite ends thereof.

In addition, from the coupled wave theory, approximate expressions of adiffraction efficiency are represented in the following manner for S-and P-polarized light, respectively;

    ηS=sin.sup.2 [(πΔnD)/λcos.sup.1/2 θ)](1)

    ηP=sin.sup.2 [(πΔnDcos.sup.1/2 θ)/λ](2)

where Δn is a refractive index modulation, D is a thickness of ahologram medium, λ is a wavelength of light, and θ is a diffractionangle (refer to FIG. 4).

As can be seen from the expressions (1) and (2), both of the approximateexpressions are functions of sin², but are different in period.

In order to realize a polarizing beam splitter (PBS) function whichdiffracts S-polarized light by almost 100% but transmits almost all ofP-polarized light therethrough using a holographic diffraction grating,conditions of a hologram are determined such that, as shown in FIG. 3(which is a diagram showing a relationship between a diffractionefficiency and a refractive index modulation of a volume typeholographic diffraction grating,) the second peak at which theefficiency for S-polarized light presents its maximum and the bottom atwhich the efficiency for P-polarized light presents its minimum maycoincide with each other.

    (πΔnD)/(λcos.sup.1/2 θ)=(3/2)·π(3)

    (πΔnDcos.sup.1/2 θ)/λ=π           (4)

Now, if the equation (4) is divided by the equation (3), then cosθ=2/3is obtained, and accordingly, θ=48.2 degrees. Further, a combination ofD and Δn is selected such that both of the equations (3) and (4) may besatisfied. For example, if D=15 μm, then Δn=0.069 should be realized.

FIG. 5 illustrates a beam shifting phenomenon when the wavelength oflight varies. When a semiconductor laser is employed as a light source,it must be taken into consideration that the wavelength is varied by atemperature, a driving current, a difference among individual elementsand so forth.

Now, if light takes an optical path indicated by a solid line when thewavelength thereof is λ, then when the wavelength is λ+Δλ(Δλ>0), thediffraction angle increases from θ to θ' so that the optical pathchanges to such as indicated by a broken line. Diffraction by 2 hologramlayers proved that a beam is shifted by Δx parallelly, but does notchange its propagating direction.

Then, the shift amount Δx of the beam is Δx=40 μm at Δλ=10 nm when thedistance tg between the two hologram layers is tg=1 mm and, in addition,θ=48.2 degrees and n=1.6. Further, in the case of Δλ<0, the shift of thebeam occurs in the opposite direction (Δx<0). However, such beam shiftas caused by a variation in wavelength described above does not make apractical problem where the distance between channels is sufficientlylarge.

(b) Description of the Second Embodiment

FIG. 6 shows a wiring scheme of a 4-input 4-output (4×4) cross connectswitch. In FIG. 6, four channels are denoted at 0, 1, 2 and 3. The4-input 4-output cross connect switch has two stages of wiringstructure.

In particular, in the 4-input 4-output cross connect switch, a 4-input4-output optical space switch is constructed such that a first opticalspace switch stage NW1 (which may be hereinafter referred to merely asfirst stage NW1) and a second optical space switch stage NW2 (which maybe hereinafter referred to merely as second stage NW2) each composed oftwo 2-input 2-output optical switches shown in FIG. 1(a) or 2 disposedin parallel to each other such that incidence faces thereof may extendin parallel to each other and the stages are stacked in a conditionwherein they are rotated by 90 degrees from each other.

More particularly, the 4-input 4-output optical space switch may beconstructed in such a manner as shown in FIGS. 7(a) and 7(b). Inparticular, at the first stage NW1, optical paths can be switchedbetween the channels 0--2 and 1--3, and at the second stage NW2, opticalpaths can be switched between the channels 0--1 and 2--3. The wiringscheme shown in FIG. 6 can be realized in this manner.

Consequently, the 4-input 4-output optical space switch is constructedwherein a shift of a beam based on a polarization condition is performedonly between adjacent channels.

Each stage section is constructed by stacking such elements as shown inFIGS. 8(a) to 8(f). It is to be noted that all of FIGS. 8(a) to 8(f) areschematic views as viewed in the incoming direction of a beam.

First, FIG. 8(a) shows a polarization controlling element SW1 forcontrolling polarization conditions of beams propagating along fourchannels independently of one another. The polarization controllingelement SW1 is constructed such that, as described hereinabove inconnection with the 2-input 2-output switch, for example, a liquidcrystal element is held between a pair of transparent electrodes and avoltage is applied across the liquid crystal element to rotate polarizedlight by 90 degrees. Such transparent electrodes are provided for eachchannel and controlled independently of one another. In other words, thepolarization controlling means is segmented in accordance with anarrangement of channels and formed integrally with one another such thatthe segments may be controlled independently of one another.

FIG. 8(b) shows a first diffraction grating layer H1. While the firstdiffraction grating layer H1 is shown divisionally in four segments,actually it is composed of two kinds of gratings. This signifies that noboundary is required between the grating for the channels 0 and 1 andthe grating for the channels 2 and 3. It is to be noted that segmentsshown in a same figure (slanting lines) represents that they haveholographic diffraction gratings having a same grating vector.

FIG. 8(c) shows a second diffraction grating layer H1'. The seconddiffraction grating layer H1' has a structure obtained by turning overthe first diffraction grating layer H1 around the axis X--X' in FIG.8(b). Also in this instance, no boundary may be provided between thegrating for the channels 0 and 1 and the grating for the channels 2 and3.

In other words, in the present arrangement, the first diffractiongrating layer H1 and the second diffraction grating layer H1' areconstructed such that a boundary is eliminated by connecting regions ofadjacent diffraction gratings which have an equal spatial frequency andare same in direction of a grating vector.

The first stage NW1 thus has a stacking structure of the polarizationcontrolling element SW1, first diffraction grating layer H1 and seconddiffraction grating layer H1' described above with reference to FIGS.8(a) to 8(c), respectively.

Meanwhile, the second stage NW2 is constructed by stacking such elementsas shown in FIGS. 8(d) to 8(f). In particular. FIG. 8(d) shows apolarization controlling element SW2 similar to the polarizationcontrolling element SW1 shown in FIG. 8(a). FIGS. 8(e) and 8(f) showdiffraction grating layers similar to those of FIGS. 8(b) and 8(c),respectively. However, the first diffraction grating layer H2 of FIG.8(e) has a structure obtained by rotating the first diffraction gratinglayer H1 of FIG. 8(b) by 90 degrees in its plane, and the seconddiffraction grating layer H2' of FIG. 8(f) has a structure obtained byrotating the second diffraction grating layer H1' of FIG. 8(c) by 90degrees in its plane.

The second stage NW2 thus has a stacking structure of the polarizationcontrolling element SW2, first diffraction grating layer H2 and seconddiffraction grating layer H2' described above with reference to FIGS.8(d) to 8(f), respectively.

Accordingly, it can be seen from the foregoing that each of the firstdiffraction grating layer H1 (H2) and the second diffraction gratinglayer H1' (H2') is constructed such that two pairs of planar diffractiongrating segments having different grating vectors are disposedtwo-dimensionally.

FIG. 9 schematically shows the 4×4 optical switch constructed bystacking such two stage structures. In the arrangement shown, amicrolens array (collimate means) 31 for collimating light emerging fromfour optical fibers LF is provided on the input side of the 4-input4-output optical space switch including the first optical space switchstage NW1 and the second optical space switch stage NW2 described above,and another microlens array (light converging means) 32 for convergingand introducing four light beams into four different optical fibers LFis provided on the output side of the 4-input 4-output optical spaceswitch. It is to be noted that reference characters G1 and G2 in FIG. 9denote each a transparent flat plate.

In this manner, the 4-input 4-output optical space switch is constructedsuch that two optical space switch stages each including polarizationcontrolling means and first and second diffraction grating layersstacked integrally with each other without having an air layer thereinare stacked integrally with each other without having an air layertherein.

In this manner, a multistage optical cross connect switch of thetwo-dimensional channel arrangement can be realized by stacking aplurality of stage structures for shifting optical paths in differentdirections each including a two-dimensional combination of unitstructures in each of which a polarization condition of light iscontrolled by means for switching a linear polarization plane of lightbetween conditions of two orthogonal directions and a pair ofdiffraction grating layers to shift optical paths. Further, since anoptical path modifying section of the optical space switch has astacking structure of a polarization controlling element and diffractiongratings, it is simple in construction and is suitable fortwo-dimensionally arranged channels. While each of diffraction gratinglayers constituting the stages has a plurality of segments, most of themare common while they are different in direction or front-rearorientation and advantageously the number of different types of parts isnot so much as the number of involved diffraction grating layers.Further, since modification of optical paths at each stage takes placebetween adjacent channels, the lengths of the optical paths requiredtherefor are minimized and it is possible to reduce the distance betweenchannels.

It is to be noted that, while the planar elements are stacked, forexample, by alternately adhering liquid crystal polarization controllingelements and transparent flat plates, which each has first and seconddiffraction grating layers on the opposite faces thereof, they may bestacked in any other suitable manner by any other suitable means.

(c) Description of the Third Embodiment

FIG. 10 shows a wiring scheme of an 8-input 8-output (8×8) cross connectswitch. In FIG. 10, eight channels are individually denoted by referencenumerals 0 to 7. The wiring scheme has four stages.

In particular, in the present arrangement, each of first to fourthoptical space switch stages NW1 to NW4 has a structure wherein four such2-input 2-output optical switches as shown in FIG. 1(a) or 2 arearranged in parallel to each other. More particularly, when the firstadjacent channel distance is represented by d and the coordinates of theorigin 0 are represented by (0, 0) as shown in FIG. 11(a), the channel 0is disposed at (0, d); the channel 1 at (d, d); the channel 2 at (d,2d); the channel 3 at (2d, 2d); the channel 4 at (d, 0); the channel 5at (2d, 0); the channel 6 at (2d, d); and the channel 7 at (3d, d), andat the first optical space switch stage (first stage) NW1, beam shiftingstructures between the channel 0--channel 4, the channel 1--channel 5,the channel 2--channel 6 and the channel 3--channel 7 as shown in FIG.11(a) are provided; beam shifting structures between the channel0--channel 2, the channel 1--channel 3, the channel 4--channel 6 and thechannel 5--channel 7 are provided at both of the second optical spaceswitch stage (second stage) NW2 and the third optical space switch stage(third stage) NW3 as shown in FIGS. 11(b) and 11(c); and beam shiftingstructures between the channel 0--channel 1, the channel 2--channel 3,the channel 4--channel 5 and the channel 6--channel 7 are provided atthe fourth optical space switch stage (fourth stage) NW4 as shown inFIG. 11(d), thereby constituting the 8-input 8-output Banyan networktype optical space switch.

Thus, an 8-input 8-output optical space switch is constructed whereinshifting of beams based on a polarization condition is performed onlybetween most adjacent channels and second most adjacent channels.

It is to be noted that, while it can be seen from the foregoing that thesecond stage NW2 and the third stage NW3 have the same wiring scheme,this is intended to produce a bypass for preventing otherwise possibleblocking.

Each of the stages is constructed by stacking such elements as shown inFIGS. 12(a) to 12(i), each of which is a schematic view as viewed in theincoming direction of a beam.

FIG. 12(a) shows a polarization controlling element SW1 for controllingpolarization conditions of beams propagating along four channelsindependently of each other. In this instance, the number of segments is8, but the structure of the polarization controlling element SW1 issimilar to that described hereinabove in connection with the 4×4 switch.In particular, the polarization controlling means is segmented inaccordance with an arrangement of the channels and the segments areformed integrally such that they may be controlled independently of oneanother.

FIG. 12(b) shows a first diffraction grating layer H1. In this instance,while the first diffraction grating layer H1 is shown divisionally ineight segments, actually it is composed of two kinds of gratings.Further, no boundary is required between the grating for the channels 0,1, 2 and 3 and the grating for the channels 4, 5, 6 and 7. It is to benoted that, also in this instance, segments shown in a same figure(slanting lines) represents holographic diffraction gratings having asame grating vector.

FIG. 12(c) shows a second diffraction grating layer H1'. Also in thisinstance, no boundary is required between the grating for the channels0, 1, 2 and 3 and the grating for the channels 4, 5, 6 and

In particular, each of the first diffraction grating layer H1 and thesecond diffraction grating layer H1' is constructed such that a boundaryis eliminated by interconnecting regions of adjacent diffractiongratings which have an equal spatial frequency and are same in directionof a grating vector.

The first stage NW1 thus has a stacking structure of the polarizationcontrolling element SW1, first diffraction grating layer H1 and seconddiffraction grating layer H1' described above with reference to FIGS.12(a) to 12(c), respectively.

Meanwhile, the second stage NW2 is constructed by stacking such elementsSW2, H2 and H2' as shown in FIGS. 12(a), 12(d) and 12(e), respectively.The third stage NW3 is constructed by stacking such elements SW3, H3 andH3' as shown in FIGS. 12(a), 12(f) and 12(g), respectively.

In this instance, the elements shown in FIGS. 12(d) and 12(f) and theelements shown in FIGS. 12(e) and 12(g) are similar diffraction gratinglayers and have structures obtained by turning over the elements shownin FIGS. 12(c) and 12(b) around the axis Y--Y', respectively.

A half-wave plate for rotating a polarization plane of light by 45degrees is interposed between the third stage NW3 and the fourth stageNW4.

Further, the fourth stage NW4 is constructed by stacking such elementsSW4, H4 and H4' shown in FIGS. 12(a), 12(h) and 12(i), respectively. Theelement H4' shown in FIG. 12(i) has a structure obtained by turning overthe element H4 shown in FIG. 12(h) around the axis Y--Y'.

While the 8-input 8-output optical space switch has a total of 8holographic diffraction grating layers shown in FIGS. 12(b) to 12(i), itinvolves only three patterns shown in FIGS. 12(b), 12(c) and 12(h).

Accordingly, each of the first diffraction grating layer H1 (H2, H3 orH4) and the second diffraction grating layer H1' (H2', H3' or H4') isconstructed such that four pairs of planar diffraction grating segmentshaving different grating vectors are arranged two-dimensionally.

FIG. 13 schematically shows the 8×8 optical switch constructed bystacking four stage structures described above as viewed in a directionperpendicular to the channels. The first diffraction grating layer H1,H2, H3 or H4 and the second diffraction grating layer H1', H2', H3' orH4' at each stage are represented in such a form that they are formed onthe opposite faces of a common transparent flat plate G1, G2, G3 or G4(refer to thick lines).

Also in this instance, a microlens array (collimate means) 31 forcollimating light emerging from eight optical fibers LF is provided onthe input side of the 8-input 8-output optical space switch includingthe first to the fourth optical space switch stages NW1 to NW4 describedabove, and another microlens array (light converging means) 32 forconverging and introducing eight light beams into eight differentoptical fibers LF is provided on the output side of the 8-input 8-outputoptical space switch. It is to be noted that reference numeral 40 inFIG. 13 denotes a half-wave plate.

The stacking structure shown in FIG. 13 can be dimensioned such that,for example, when the channel distance is 1.8 mm, the input face has asize of 7.2×5.4 mm and the length in a thicknesswise direction is about18 mm or so. However, the dimensions are only of an effective portion ofthe optical path polarization switching section but do not includedimensions of wires for driving the polarization controlling elementsand coupling portions to the optical fibers.

In this manner, the 8-input 8-output optical space switch is constructedsuch that four optical space switch stages each including polarizationcontrolling means and first and second diffraction grating layersstacked integrally with each other without having an air layer thereinare stacked integrally with each other without having an air layertherein.

In this manner, a multistage optical cross connect switch of thetwo-dimensional channel arrangement can be realized by stacking one ormore wavelength plates and a plurality of stage structures for shiftingoptical paths in different directions, each including a two-dimensionalcombination of unit structures in each of which a polarization conditionof light is controlled by means for switching a linear polarizationplane of light between conditions of two orthogonal directions and apair of diffraction grating layers to shift optical paths. Further,since an optical path modifying section of the optical space switch hasa stacking structure of a polarization controlling element anddiffraction gratings, it is simple in construction and is suitable fortwo-dimensionally arranged channels. While each of diffraction gratinglayers constituting the stages has a plurality of segments, most of themare common while they are different in direction or front-rearorientation and advantageously the number of different types of parts isnot so much as the number of involved diffraction grating layers.Further, since modification of optical paths at each stage takes placebetween adjacent channels, the lengths of the optical paths requiredtherefor are minimized and it is possible to reduce the distance betweenchannels.

It is to be noted that the size of a segment may be designed withdimensions taking a diameter of a beam, a shift of a beam involved invariation in wavelength and a margin into consideration. Therefore,while regions in which diffraction gratings are present are shown in amutually contacting form in FIGS. 8 and 12, when it is taken intoconsideration that it is desirable to minimize the diffraction gratings,such construction as shown in FIG. 14 may be employed wherein, in orderto minimize a margin, a region in which no diffraction grating ispresent is provided at a boundary of each segment such that all channelsmay be surrounded, at a first diffraction grating layer Hi (i is anatural number) and a second diffraction grating layer Hi', by aboundary having a predetermined width in which no diffraction grating isformed, in order to reduce crosstalk.

(d) Description of the Fourth Embodiment

FIG. 15 shows an optical space switch device according to a fourthpreferred embodiment of the present invention. The optical space switchdevice of the present embodiment has an equivalent circuit structure ofan 11 stage cross Banyan network. The optical space switch deviceincludes unit switches each of which is such a 2-input 2-output opticalswitch as described hereinabove with reference to FIG. 1(a).

The optical space switch device according to the present embodimenthaving an equivalent circuit structure of an 11 stage cross Banyannetwork can be constructed by stacking a wavelength plate and aplurality of stage structures for shifting optical paths in differentdirections each including a two-dimensional combination of unitstructures in each of which a polarization condition of light iscontrolled by such means 10 for switching a linearly polarized lightbeam between conditions of two orthogonal directions and a pair ofdiffraction grating layers 22 and 23 as described above. With theconstruction, the lengths of beams and the difference between theoptical lengths of the beams can be minimized, and a multistage opticalcross switch of a two-dimensional channel arrangement can be realized.

In short, an optical space switch apparatus having an equivalent circuitstructure of an 11 stage cross Banyan network is constructed by stacking11 optical space switch stages each including a plurality of such2-input 2-output optical switches as shown in FIG. 1(a) or 2, which aredisposed such that planes defined by each 2 parallel optical axesthereof may extend in parallel to each other.

Then, in order to realize the wiring scheme equivalent to the wiringscheme of the 16-input 16-output eleven stage cross connect switch shownin FIG. 15 using a 2-input 2-output optical switch making the basicconstruction described above, it is necessary to stack suitable hologramarrays for polarization of beams for each stage, and besides, sixteeninput beams are arranged two-dimensionally so as to achieve matchingwith a multichannel multistage switching operation of the hologramarrays.

When 16 input beams are arranged two-dimensionally as shown in FIG. 16,that is, when, representing the adjacent channel distance by d anddisposing the channel 0 (CH0) at the origin 0 (0, 0), the channel 1(CH1) is disposed at (0, -2d); the channel 2 (CH2) at (2d, 0); thechannel 3 (CH3) at (2d, -2d); the channel 4 (CH4) at (d, -d) ; thechannel 5 (CH5) at (d, -3d); the channel 6 (CH6) at (3d, -d) ; thechannel 7 (CH7) at (3d, -3d); the channel 8 (CH8) at (d, 0); the channel9 (CH9) at (d, -2d); the channel 10 (CH10) at (3d, 0); the channel 11(CH11) at (3d, -2d); the channel 12 (CH12) at (0, -d); the channel 13(CH13) at (0, -3d); the channel 14 (CH14) at (2d, -d); and the channel15 (CH15) at (2d, -3d), as shown in FIG. 17, at the first, fourth,seventh and tenth optical space switch stages (first, fourth, seventhand tenth stages), a beam can be shifted between the channels 0--2,4--6, 1--3, 5--7, 8--10, 12--14, 9--11 and 13--15; a beam can be shiftedbetween the channels 0--1, 4--5, 2--3, 6--7, 12--13, 8--9, 14--15 and10--11 at the second, fifth, eighth and eleventh optical space switchstages (second, fifth, eighth and eleventh stages); a beam can beshifted between the channels 0--4, 1--5, 2--6, 3--7, 8--12, 9--13,10--14 and 11--15 at the third and ninth optical space switch stages(third and ninth stages); and a beam can be shifted between the channels0--8, 12--4, 1--9, 13--5, 2--10, 14--6, 3--11 and 15--7 at the sixthoptical space switch stage (sixth stage).

The equivalent circuit of FIG. 15 is thus constructed. Further, with anoptical channel structure wherein the equivalent circuit can be realizedby a combination of the basic constructions of a thin film multistageoptical space switch described above, if incidence of S-polarized lightis assumed, then a non-blocking cross connect routing algorithm ispresent and can be described in the following manner.

Where NB(I) is the Ith bit of the binary represented address of eachnode at each stage, FB(J) is the Jth bit of the binary representedaddress of a destination node, PS is the polarization of the input beamat each node having the value "0" when the polarization of the inputbeam to the node is P-polarization but having the value "1" when suchpolarization is S-polarization, and SC is the state of the polarizationcontrolling switch (=0; OFF and =1; ON), polarization switch setting isprovided such that.

for the first, fourth, seventh and tenth stages,

    SC=PS XOR (NB(3) XOR FB(3))

for the second, fifth, eighth and eleventh stages,

    SC=PS XOR (NB(4) XOR FB(4))

for the third and ninth stages,

    SC=PS XOR (NB(2) XOR FB(2)), and

for the sixth stage.

    SC=PS XOR (NB(1) XOR FB(1))

where X XOR Y signifies exclusive OR of X and Y.

With such construction, when the two-dimensional arrangement of channelsfor input beams is determined in such a manner as described above, ifroutes of beams are represented in permutation of channel numbers ofcorresponding beam spots of the layers, then the following 16 exchangeroutes of the equivalent circuit are available:

(1) 0--2--3--7--5--4--12--14--15--11--9--8

(2) 1--3--2--6--4--5--13--15--14--10--8--9

(3) 2--0--1--5--7--6--14--12--13--9--11--10

(4) 3--1--0--4--6--7--15--13--12--8--10--11

(5) 4--6--7--3--1--0--8--10--11--15--13--12

(6) 5--7--6--2--0--1--g--11--10--14--12--13

(7) 6--4--5--1--3--2--10--8--g--13--15--14

(8) 7--5--4--0--2--3--11--9--8--12--14--15

(9) 8--10--11--15--13--12--4--6--7--3--1--0

(10) 9--11--10--14--12--13--5--7--6--2--0--1

(11) 10--8--9--13--15--14--6--4--5--1--3--2

(12) 11--9--8--12--14--15--7--5--4--0--2--3

(13) 12--14--15--11--9--8--0--2--2--7--5--4

(14) 13--15--14--10--8--9--1--3--2--6--4--5

(15) 14--12--13--g--11--10--2--0--1--5--7--6

(16) 15--13--12--8--10--11--3--1--0--4--6--7

The routes given above can all be realized by the equivalent circuit ofFIG. 15 and correspond one by one to channel connections constructed bythe hologram arrays of FIG. 17, and can thus be cross connect routednon-blockingly by ON/OFF control of the polarization controllingelements.

Accordingly, if the exchange routes of the channels are traced, then itcan be seen that routes the equivalent circuit and the two-dimensionalmultilayer switch coincide with each other, which is an effectiveconstruction.

In this instance, while actually there are 16 factorial (16!) crossconnect routes, since here the structure is such that a 4-input 4-outputnon-blocking network structure having a cross connect routing propertyis expanded to a 16-input 16-output scheme by butterfly connection whilemaintaining the non-blocking property, the non-blocking property isassured.

In this manner, since a small size multi-input multi-output opticalspace switch of the thin film stacking structure is constructed by acombination of polarization controlling elements and hologramdiffraction elements, a two-dimensional arrangement of 16 beams isavailable, and non-blocking cross connect routing of a 16-input 11 stagecross Banyan network can be realized optically by polarization control.

(e) Description of the Fifth Embodiment

FIG. 18 shows an optical space switch device according to a fifthpreferred embodiment of the present invention. The optical space switchdevice of the present embodiment has an equivalent circuit structure ofa 9 stage expanded modified Banyan network (the equivalent circuit isequivalent to a wiring scheme of a 16-input 16-output 9 stage crossconnect switch). In this instance, the optical space switch devicehaving an equivalent circuit structure of a 9 stage expanded modifiedBanyan network is constructed by stacking 9 optical space switch stageseach including a plurality of such 2-input 2-output optical switches asshown in FIG. 1(a) or 2, which are disposed such that planes defined byeach 2 parallel optical axes thereof may extend in parallel to eachother.

In this instance, in order to realize the wiring scheme described abovewith such a basic construction as shown in FIG. 1(a) or 2, when 16 inputbeams are arranged two-dimensionally as shown in FIG. 19, that is, when,representing the adjacent channel distance by d and disposing thechannel 0 (CH0) at the origin 0 (0, 0) on the light incidence plane, thechannel 1 (CH1) is disposed at (d, -d); the channel 2 (CH2) at (0, -2d);the channel 3 (CH3) at (d, -3d); the channel 4 (CH4) at (2d, 0); thechannel 5 (CH5) at (3d, -d); the channel 6 (CH6) at (2d, -2d); thechannel 7 (CH7) at (3d, -3d); the channel 8 (CH8) at (d, 0); the channel9 (CH9) at (0, -d); the channel 10 (CH10) at (d, -2d); the channel 11(CH11) at (0, -3d); the channel 12 (CH12) at (3d, 0); the channel 13(CH13) at (2d, -d); the channel 14 (CH14) at (3d, -2d); and the channel15 (CH15) at (2d, -3d), the hologram arrays at the individual stages aredisposed such that, at the first and sixth optical space switch stages(first and sixth stages), a beam can be shifted between the channels0--4, 1--5, 2--6, 3--7, 8--12, 9--13, 10--14 and 11--15; a beam can beshifted between the channels 0--2, 1--3, 4--15 and 12--14 at the second,third, seventh and eighth optical space switch stages (second, third,seventh and eighth stages); a beam can be shifted between the channels0--1, 2--3, 4--5, 6--7, 8--9, 10--11, 12--13 and 14--15 at the fourthand ninth optical space switch stages (fourth and ninth stages); and abeam can be shifted between the channels 0--8, 1--9, 2--10, 3--11,4--12, 5--13, 6--14 and 7--15 at the fifth optical space switch stage(fifth stage).

The equivalent circuit of FIG. 18 is thus constructed. Further, with anoptical channel structure wherein the equivalent circuit can be realizedby a combination of the basic constructions of a thin film multistageoptical space switch, if incidence of S-polarized light is assumed, thena non-blocking cross connect routing algorithm is present and can bedescribed in the following manner.

Where NB(I) is the Ith bit of the binary represented address of eachnode at each stage, FB(J) is the Jth bit of the binary representedaddress of a destination node, PS is the polarization of the input beamat each node having the value "0" when the polarization of the inputbeam to the node is P-polarization but having the value "1" when suchpolarization is S-polarization, and SC is the state of the polarizationcontrolling switch (=0; OFF and =1; ON), polarization switch setting isprovided such that,

for the first, third, fourth, sixth, eighth and ninth stages.

    SC=PS XOR (NB(M) XOR FB(M))

where M=2, 3, 4, 2, 3, 4 in this order for the stages.

for the second and seventh stages,

    SC=PS XOR (NB(3) XOR FB(3)), and

for the fifth stage,

    SC=PS XOR (NB(1) XOR FB(1))

where, also in this instance, X XOR Y signifies exclusive OR of X and Y.

With such construction, when the two-dimensional arrangement of channelsfor input beams is determined in such a manner as described above, ifroutes of beams are represented in permutation of channel numbers ofcorresponding beam spots of the layers, then the following 16 exchangeroutes of the equivalent circuit are available;

(1) 0--4--6--4--5--13--9--11--9--8

(2) 1--5--7--5--4--12--8--10--8--9

(3) 2--6--4--6--7--15--11--9--11--10

(4) 3--7--5--7--6--14--10--8--10--11

(5) 4--0--2--0--1--9--13--15--13--12

(6) 5--1--3--1--0--8--12--14--12--13

(7) 6--2--0--2--3--11--15--13--15--14

(8) 7--3--1--3--2--10--14--12--14--15

(9) 8--12--14--12--13--5--1--3--1--0

(10) 9--13--15--13--12--4--0--2--0--1

(11) 10--14--12--14--15--7--3--1--3--2

(12) 11--15--13--15--14--6--2--0--2--3

(13) 12--8--10--8--9--1--5--7--5--4

(14) 13--9--11--9--8--0--4--6--4--5

(15) 14--10--8--10--11--3--7--5--7--6

(16) 15--11--9--11--10--2--6--4--6--7

The routes given above can all be realized by the equivalent circuit ofFIG. 18 and correspond one by one to channel connections constructed bythe hologram arrays of FIG. 20, and can thus be cross connect routednon-blockingly by ON/OFF control of the polarization controllingelements.

Accordingly, also in this instance, if the exchange routes of thechannels are traced, then it can be seen that routes in the equivalentcircuit and the two-dimensional multilayer switch coincide with eachother, which is an effective construction. Further, while actually thereare 16 factorial (16!) cross connect routes also in this instance, thenon-blocking property is assured due to a similar reason as describedabove.

It is to be noted that the present holographic Banyan optical spaceswitch is embodied in a 9 stage stacking structure as shown in FIG. 22.Here, a polarization controlling element SWi at each stage NWi is formedin a condition surrounded by a pair of two-dimensional transparentelectrodes, and the present holographic Banyan stacking structure has astacking structure wherein blocks each formed from a transparent glassplate Gi and first and second diffraction grating layers Hi and Hi'formed on the opposite faces of the transparent glass plate Gi and thepolarization controlling elements SWi are alternately adhered to eachother. It is to be noted that a half-wave plate Wj is interposed betweeneach necessary adjacent ones of the stages. Incident light and emergentlight are introduced by optical fiber arrays FA, and a pair of microlensarrays 31 and 32 are provided on the opposite sides of the stages inorder to obtain collimated light. FIG. 21 shows a nine stage stackedsolid structure.

A two-dimensional arrangement of 16 beams is available also with theconstruction described above, and non-blocking cross connect routing ofa 16-input nine stage expanded modified Banyan network can be realizedoptically by polarization control.

(f) Description of the Sixth Embodiment

Subsequently, a sixth preferred embodiment of the present invention willbe described. The sixth embodiment provides an optical space switchdevice having an equivalent circuit structure of a 2^(n) -input (n is aninteger equal to or greater than 4) expanded modified Banyan network.

In addition, the fundamental principle of the present invention can beapplied, when an equivalent circuit of a multistage connection networkis given, to implementation of the same if it can be constructed by acombination of 2-input 2-output switches. Particularly, using a thinfilm multistage optical space switch of the 8-input modified Banyannetwork type as a basic construction module, it can be expanded tooptical space switches of the 16-input, 32-input or 64-input type or soas shown in FIG. 23 while maintaining the non-blocking property of the8-input modified Banyan network. The 2^(n) -input expanded modifiedBanyan network shown in FIG. 23 is constructed in this manner.

Referring to FIG. 23, a circuit 100 is equivalent to the 16-input 9stage expanded modified Banyan network shown in FIG. 9 which isconsidered to be an aggregate of 8-input modified Banyan networks, and acircuit 200 includes four such 16-input 9 stage expanded modified Banyannetworks 100.

In this instance, the polarization controlling algorithm for an 8-inputmodified Banyan network is successively expanded to allow non-blockingcross connect routing for 2^(n) inputs.

In particular, the polarization controlling algorithm for an 8-inputmodified Banyan network is such as follows. First, where NB(I) is theIth bit of the binary represented address of each node at each stage.FB(J) is the Jth bit of the binary represented address of a destinationnode, PS is the polarization of the input beam at each node having thevalue "0" when the polarization of the input beam to the node isP-polarization but having the value "1" when such polarization isS-polarization, and SC is the state of the polarization controllingswitch (=0; OFF and =1; ON), polarization switch setting is providedsuch that,

for the first, third and fourth stages,

    SC=PS XOR (NB(M) XOR FB(M))

where M=1, 2, 3 in this order for the stages, and

for the second stage,

    SC=PS XOR FB(2)

where, also in this instance, X XOR Y signifies exclusive OR of X and Y.

Further, a method of successively expanding an 8-input two-dimensionalarrangement to 16-, 32- and 64-input two-dimensional arrangements ispresent as shown in FIG. 24 and represented in the following manner.

First, when N of 2^(N+2) inputs (N=2m:m=1, 2, 3 . . . ) is an oddnumber:

(1) A second arrangement which is horizontally symmetrical with anoriginal arrangement of 2^(N+2) channels is made separately.

(2) Channel numbers equal to or greater than 2^(N+2) are applied to thesecond channel arrangement while maintaining the order of rows and theorder of columns in each row of the original channel arrangement.

(3) The two channel arrangements are overlaid to make a furtherarrangement of 2^(N+3) channels.

On the other hand, when N of the 2^(N+2) inputs is an even number:

(1) A second arrangement which is the same as an original arrangement of2^(N+2) channels is made separately.

(2) Channel numbers equal to or greater than 2^(N+2) are applied to thesecond channel arrangement while maintaining the order of rows and theorder of columns in each row of the original channel arrangement.

(3) The two channel arrangements are overlaid in a displaced conditionby one half the minimum channel distance d in two orthogonal directionsto make a further arrangement of 2^(N+3) channels.

Thus, in the sixth embodiment, the multi-input multi-output opticalspace switch constructed based on the basic switch shown in FIG. 1(a) or(2) can be regarded as an optical space switch device which has anequivalent circuit of a 2^(n) -input expanded modified Banyan networkwhich can be realized by successively expanding 8-input modified Banyannetworks, which can be realized by a combination of such basic switchesand are used as a basic construction module, by butterfly connection,and as an optical space switch device which has a polarizationcontrolling algorithm which is based on a polarization controllingalgorithm which realizes non-blocking cross connect routing of an8-input modified Banyan network and can be successively expanded andapplied to 2^(n) -input expanded modified Banyan networks, and furtheras an expansion of a two-dimensional dimensional arrangement scheme of2^(n+2) beams incident to an optical channel structure which can berealized in accordance with an equivalent circuit of the 2^(n) -inputexpanded modified Banyan network described above.

In this manner, the optical space switch of the sixth embodiment havingexpansibility of a two-dimensional arrangement has optical channelsrepresented by an equivalent circuit of a 2^(N+2) -input expandedmodified Banyan network and has a polarization controlling algorithmwhich makes non-blocking cross connect routing possible.

Non-blocking cross connect routing of a 2^(N+2) -input expanded modifiedBanyan network can be realized optically even with the construction.

The present invention is not limited to the specifically describedembodiment, and variations and modifications may be made withoutdeparting from the scope of the present invention.

What is claimed is;
 1. An optical space switch, comprising;four opticalspace switch stages stacked to form an 8-input 8-output Banyan networktype optical space switch having channels 0, 1, 2, 3, 4, 5, 6 and 7extending therethrough, wherethe distance between the closest adjacentchannels is represented by d and the coordinates of an origin arerepresented by (0, 0), the channel 0 is disposed at the coordinates (0,d), the channel 1 is disposed at the coordinates (d, d), the channel 2is disposed at the coordinates (d, 2d), the channel 3 is disposed at thecoordinates (2d, 2d), the channel 4 is disposed at the coordinates (d,0), the channel 5 is disposed at the coordinates (2d, 0), the channel 6is disposed at the coordinates (2d, d), and the channel 7 is disposed atthe coordinates (3d, d), beam shifting structures exist in the firstoptical space switch stage between the channel 0 and the channel 4,between the channel 1 and the channel 5, between the channel 2 and thechannel 6 and between the channel 3 and the channel 7, beam shiftingstructures exist in both the second and third optical space switchstages between the channel 0 and the channel 2, between the channel 1and the channel 3, between the channel 4 and the channel 6 and betweenthe channel 5 and the channel 7, beam shifting structures exist in thefourth optical space switch stage between the channel 0 and the channel1, between the channel 2 and the channel 3, between the channel 4 andthe channel 5 and between the channel 6 and the channel 7, and eachstage includes four 2-input 2-output optical switches, each of the2-input 2-output optical switches defining first and second optical axesextending therethrough in a parallel, spaced relationship, and havingrespective, first and second light input positions at which first andsecond lights are received and respective first and second light outputpositions, the 2-input 2-output optical switches of each stage arearranged in a common plane with the first and second optical axes ofeach switch being in parallel with the first and second optical axes ofthe other switches in the respective stage, each 2-input 2-outputoptical switch comprisingpolarization controlling means, disposedtransversely to the first and second optical axes and through whichextend the first and second optical axes, for switching a polarizationplane of light transmitted therethrough from one to another of first andsecond orthogonal polarization directions; and optical path shiftingmeans, disposed transversely to the first and second optical axes, andbetween the polarization controlling means and the first and secondlight output positions, for receiving first and second lightsrespectively transmitted through the polarization controlling meansalong the first and second optical axes, and for selectively outputtingthe received first and second lights at the first and second lightoutput positions, respectively, when the polarization plane of the firstand second lights is in the first orthogonal polarization direction, andfor outputting the first and second lights at the second and first lightoutput positions, respectively, when the polarization plane of the firstand second lights is in the second orthogonal polarization direction. 2.An optical space switch as claimed in claim 1, further comprising meansinterposed between the third and fourth optical space switch stages forrotating a polarization plane of polarized light by 45 degrees.
 3. Anoptical space switch comprising;eleven optical space switch stagesstacked to form an equivalent structure of an eleven stage cross Banyannetwork and having channels 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,13, 14 and 15 extending therethrough, wherethe distance between theclosest adjacent channels is represented by d and the coordinates of anorigin are represented by (0, 0), the channel 0 is disposed at thecoordinates (0,0), the channel 1 is disposed at the coordinates (0,-2d), the channel 2 is disposed at the coordinates (2d, 0), the channel3 is disposed at the coordinates (2d, -2d), the channel 4 is disposed atthe coordinates (d, -d), the channel 5 is disposed at the coordinates(d, -3d), the channel 6 is disposed at the coordinates (3d, -d), thechannel 7 is disposed at the coordinates (3d, -3d), the channel 8 isdisposed at the coordinates (d, 0), the channel 9 is disposed at thecoordinates (d, -2d), the channel 10 is disposed at the coordinates (3d,0), the channel 11 is disposed at the coordinates (3d, -2d), the channel12 is disposed at the coordinates (0, -d), the channel 13 is disposed atthe coordinates (0, -3d), the channel 14 is disposed at the coordinates(2d, -d), and the channel 15 is disposed at the coordinates (2d, -3d), abeam can be shifted at the first, fourth, seventh and tenth opticalspace switch stages between the channel 0 and the channel 2, between thechannel 4 and the channel 6, between the channel 1 and the channel 3,between the channel 5 and the channel 7, between the channel 8 and thechannel 10, between the channel 12 and the channel 14, between thechannel 9 and the channel 11 and between the channel 13 and the channel15, a beam can be shifted at the second, fifth, eighth and eleventhoptical space switch stages between the channel 0 and the channel 1,between the channel 4 and the channel 5, between the channel 2 and thechannel 3, between the channel 6 and the channel 7, between the channel12 and the channel 13, between the channel 8 and the channel 9, betweenthe channel 14 and the channel 15 and between the channel 10 and thechannel 11, a beam can be shifted at the third and ninth optical spaceswitch stages between the channel 0 and the channel 4, between thechannel 1 and the channel 5, between the channel 2 and the channel 6,between the channel 3 and the channel 7, between the channel 8 and thechannel 12, between the channel 9 and the channel 13, between thechannel 10 and the channel 14 and between the channel 11 and the channel15, a beam can be shifted at the sixth optical space switch stagebetween the channel 0 and the channel 8, between the channel 12 and thechannel 4, between the channel 1 and the channel 9, between the channel13 and the channel 5, between the channel 2 and the channel 10, betweenthe channel 14 and the channel 6, between the channel 3 and the channel11 and between the channel 15 and the channel 7, NB(I) is the Ith bit ofa binary represented address of each node at each stage, FB(J) is theJth bit of the binary represented address of a destination node, PS isthe polarization of an input beam of light at each node having the value"0" when the polarization of the input beam to the node isP-polarization but having the value "1" when such polarization isS-polarization, and SC is the state of the polarization controllingswitch, polarization switch setting is provided such that,for the first,fourth, seventh and tenth stages

    SC=PS XOR (NB(3) XOR FB(3)),

for the second, fifth, eighth and eleventh stages

    SC=PS XOR (NB(4) XOR FB(4)),

for the third and ninth stages

    SC=PS XOR (NB(2) XOR FB(2)),

and for the sixth stage

    SC=PS XOR (NB(i) XOR FB(1)),

where X XOR Y signifies an exclusive OR operation of X and Y, each stageincludes 2-input 2-output optical switches, each of the 2-input 2-outputoptical switches defining first and second optical axes extendingtherethrough in a parallel, spaced relationship, and having respective,first and second light input positions at which first and second lightsare received and respective first and second light output positions, the2-input 2-output optical switches of each stage are arranged in a commonplane with the first and second optical axes of each switch being inparallel with the first and second optical axes of the other switches inthe respective stage, each 2-input 2-output optical switchcomprisingpolarization controlling means, disposed transversely to thefirst and second optical axes and through which extend the first andsecond optical axes, for switching a polarization plane of lighttransmitted therethrough from one to another of first and secondorthogonal polarization directions, and optical path shifting means,disposed transversely to the first and second optical axes, and betweenthe polarization controlling means and the first and second light outputpositions, for receiving first and second lights respectivelytransmitted through the polarization controlling means along the firstand second optical axes, and for selectively outputting the receivedfirst and second lights at the first and second light output positions,respectively, when the polarization plane of the first and second lightsis in the first orthogonal polarization direction, and for outputtingthe first and second lights at the second and first light outputpositions, respectively, when the polarization plane of the first andsecond lights is in the second orthogonal polarization direction.
 4. Anoptical space switch comprising;nine optical space switch stages stackedto form an equivalent structure of a nine stage cross Banyan network andhaving channels 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 and 15extending therethrough, wherethe distance between the closest adjacentchannels is represented by d and the coordinates of an origin arerepresented by (0, 0), the channel 0 is disposed at the coordinates (0,0), the channel 1 is disposed at the coordinates (d, -d), the channel 2is disposed at the coordinates (0, -2d), the channel 3 is disposed atthe coordinates (d, -3d), the channel 4 is disposed at the coordinates(2d, 0), the channel 5 is disposed at the coordinates (3d, -d), thechannel 6 is disposed at the coordinates (2d, -2d), the channel 7 isdisposed at the coordinates (3d, -3d), the channel 8 is disposed at thecoordinates (d, 0), the channel 9 is disposed at the coordinates (0,-d), the channel 10 is disposed at the coordinates (d, -2d), the channel11 is disposed at the coordinates (0, -3d), the channel 12 is disposedat the coordinates (3d, 0), the channel 13 is disposed at thecoordinates (2d, -d), the channel 14 is disposed at the coordinates (3d,-2d), and the channel 15 is disposed at the coordinates (2d, -3d), abeam can be shifted at the first and sixth optical space switch stagesbetween the channel 0 and the channel 4, between the channel 1 and thechannel 5, between the channel 2 and the channel 6, between the channel3 and the channel 7, between the channel 8 and the channel 12, betweenthe channel 9 and the channel 13, between the channel 10 and the channel14 and between the channel 11 and the channel 15, a beam can be shiftedat the second, third, seventh and eighth optical space switch stagesbetween the channel 0 and the channel 2, between the channel 1 and thechannel 3, between the channel 4 and the channel 6, between the channel5 and the channel 7, between the channel 9 and the channel 11, betweenthe channel 8 and the channel 10, between the channel 13 and the channel15 and between the channel 12 and the channel 14, a beam can be shiftedat the fourth and ninth optical space switch stages between the channel0 and the channel 1, between the channel 2 and the channel 3, betweenthe channel 4 and the channel 5, between the channel 6 and the channel7, between the channel 8 and the channel 9, between the channel 10 andthe channel 11, between the channel 12 and the channel 13 and betweenthe channel 14 and the channel 15, a beam can be shifted at the fifthoptical space switch stage between the channel 0 and the channel 8,between the channel 1 and the channel 9, between the channel 2 and thechannel 10, between the channel 3 and the channel 11, between thechannel 4 and the channel 12, between the channel 5 and the channel 13,between the channel 6 and the channel 14 and between the channel 7 andthe channel 15, where NB(I) is the Ith bit of the binary representedaddress of each node at each stage, FB(J) is the Jth bit of the binaryrepresented address of a destination node, PS is the polarization of aninput beam of light at each node having the value "0" when thepolarization of the input beam to the node is P-polarization but havingthe value "1" when such polarization is S-polarization, and SC is thestate of the polarization controlling switch, polarization switchsetting is provided such that,for the first, third, fourth, sixth,eighth and ninth stages

    SC=PS XOR (NB(M) XOR FB(M)),

where M=2, 3, 4, 2, 3, 4 in this order for the stages, for the secondand seventh stages

    SC=PS XOR (NB(3) XOR FB(3)), and

for the fifth stage,

    SC=PS XOR (NB(1) XOR FB(1))

where X XOR Y signifies exclusive OR operation of X and Y, each stageincludes 2-input 2-output optical switches, each of the 2-input 2-outputoptical switches defining first and second optical axes extendingtherethrough in a parallel, spaced relationship, and having respective,first and second light input positions at which first and second lightsare received and respective first and second light output positions, the2-input 2-output optical switches of each stage are arranged in a commonplane with the first and second optical axes of each switch being inparallel with the first and second optical axes of the other switches inthe respective stage, each 2-input 2-output optical switchcomprisingpolarization controlling means, disposed transversely to thefirst and second optical axes and through which extend the first andsecond optical axes, for switching a polarization plane of lighttransmitted therethrough from one to another of first and secondorthogonal polarization directions, and optical path shifting means,disposed transversely to the first and second optical axes, and betweenthe polarization controlling means and the first and second light outputpositions, for receiving first and second lights respectivelytransmitted through the polarization controlling means along the firstand second optical axes, and for selectively outputting the receivedfirst and second lights at the first and second light output positions,respectively, when the polarization plane of the first and second lightsis in the first orthogonal polarization direction, and for outputtingthe first and second lights at the second and first light outputpositions, respectively, when the polarization plane of the first andsecond lights is in the second orthogonal polarization direction.
 5. Anoptical space switch comprising;a plurality of optical space switchstages, four optical space switch stages being stacked to form anequivalent structure of an eight-input modified Banyan network, and aplurality of the equivalent structures of an eight-input modified Banyannetwork being combined to form an equivalent structure of a 2^(n) -inputexpanded modified Banyan network, wherein,in each of the equivalentstructures of an eight-input modified Banyan network, NB(I) is the Ithbit of a binary represented address of each node at each stage, FB(J) isa Jth bit of a binary represented address of a destination node, PS isthe polarization of an input beam of light at each node and having thevalue "0" when the polarization of the input beam to the node isP-polarization and having the value "1" when the polarization isS-polarization, and SC is the state of a polarization controllingswitch, polarization switch setting is provided such that,for the first,third and fourth stages,

    SC=PS XOR (NB (M) XOR FB(M)),

where M=1, 2, 3 in this order for the stages, and for the second stage,

    SC=PS XOR FB(2),

where X XOR Y signifies an exclusive OR operation of X and Y, each stageincludes 2-input 2-output optical switches, each of the 2-input 2-outputoptical switches defining first and second optical axes extendingtherethrough in a parallel, spaced relationship, and having respective,first and second light input positions at which first and second lightsare received and respective first and second light output positions, the2-input 2-output optical switches of each stage are arranged in a commonplane with the first and second optical axes of each switch being inparallel with the first and second optical axes of the other switches inthe respective stage, each 2-input 2-output optical switchcomprisingpolarization controlling means, disposed transversely to thefirst and second optical axes and through which extend the first andsecond optical axes, for switching a polarization plane of lighttransmitted therethrough from one to another of first and secondorthogonal polarization directions, and optical path shifting means,disposed transversely to the first and second optical axes, and betweenthe polarization controlling means and the first and second light outputpositions, for receiving first and second lights respectivelytransmitted through the polarization controlling means along the firstand second optical axes, and for selectively outputting the receivedfirst and second lights at the first and second light output positions,respectively, when the polarization plane of the first and second lightsis in the first orthogonal polarization direction, and for outputtingthe first and second lights at the second and first light outputpositions, respectively, when the polarization plane of the first andsecond lights is in the second orthogonal polarization direction.
 6. Anoptical space switch as claimed in claim 5, wherein the number of inputsis given by 2^(N+2), N being a positive integral number, and, when N isan odd number, a second arrangement which is horizontally symmetricalwith an original arrangement of 2^(N+2) channels is first madeseparately, and then channel numbers equal to or greater than 2^(N+2)are applied to the second channel arrangement while maintaining theorder of rows and the order of columns in each row of the originalchannel arrangement, whereafter the two channel arrangements areoverlaid to make a further arrangement of 2^(N+3) channels, therebyexpanding an equivalent structure of an eight-input modified Banyannetwork by combining a plurality of equivalent structures of aneight-input modified Banyan network.
 7. An optical space switch deviceas claimed in claim 5, wherein the number of inputs is given by 2^(N+2),N being a positive integral number, and, when N is an even number, asecond arrangement which is the same as an original arrangement of2^(N+2) channels is made separately, and then channel numbers equal toor greater than 2^(N+2) are applied to the second channel arrangementwhile maintaining the order of rows and the order of columns in each rowof the original channel arrangement, whereafter the two channelarrangements are overlaid in a displaced condition by one half theminimum channel distance d in two orthogonal directions to make afurther arrangement of 2^(N+3) channels, thereby expanding an equivalentstructure of an eight-input modified Banyan network by combining of aplurality of equivalent structures of an eight-input modified Banyannetwork.